Predicting Direct-Specimen SARS-CoV-2 Assay Performance Using Residual Patient Samples.

BACKGROUND: Diagnostic sensitivities of point-of-care SARS-CoV-2 assays depend on specimen type and population-specific viral loads. Evaluation of these assays require "direct" specimens from paired-swab studies rather than more accessible residual specimens in viral transport media (VTM). METHODS: Residual VTM and limit-of-detection studies were conducted on Abbott ID NOW™ COVID-19, Quidel Sofia 2™ SARS Antigen FIA, and DiaSorin Simplexa™ COVID-19 Direct assays, with cycle threshold (CT) adjustments to approximate direct-specimen testing based on gene-target doubling each PCR cycle. Logistic regression was used to model assay performance by specimen CT. These models were applied to CT distributions of symptomatic and asymptomatic populations presenting to emergency services to predict the percentage of specimens that would be detected by each assay. A 96-sample paired-swab study was conducted to confirm model results. RESULTS: When using direct nasopharyngeal samples and fit with either VTM or limit-of-detection data, percent positivities for ID NOW (symptomatic 94.9%/97.4%; asymptomatic 88.4.0%/89.6%) and Simplexa (symptomatic 97.8%/97.2%; asymptomatic 91.1%/90.8%) were predicted to be similar. Likewise, percent positivities for ID NOW with direct nasal specimens (symptomatic 77.8%; asymptomatic 64.5%) and, fit with VTM data, Sofia 2 with direct nasopharyngeal specimens (symptomatic 76.6%, asymptomatic 60.3%) were similar. The paired-swab study comparing direct nasopharyngeal specimens on ID NOW and nasopharyngeal VTM specimens on Simplexa showed 99% concordance. CONCLUSIONS: Assay performance can be modeled as dependent on viral load, fit using laboratory bench study results, and adjusted to account for direct-specimen testing. When using nasopharyngeal specimens, direct testing on Abbott ID NOW and VTM testing on DiaSorin Simplexa have similar performance.

Severe Acute Respiratory Syndrome Coronavirus 2 Surveillance in Decedents in a Large, Urban Medical Examiner's Office.

BACKGROUND: Given the challenges in implementing widespread testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there is increasing interest in alternative surveillance strategies. METHODS: We tested nasopharyngeal swabs from 1094 decedents in the Wayne County Medical Examiner's Office for SARS-CoV-2. All decedents were assessed using a coronavirus disease 2019 (COVID-19) checklist, and decedents flagged using the checklist (298) were preferentially tested. A random sample of decedents not flagged using the checklist were also tested (796). We statistically analyzed the characteristics of decedents (age, sex, race, and manner of death), differentiating between those flagged using the checklist and not and between those SARS-CoV-2-positive and not. RESULTS: A larger percentage of decedents overall were male (70% vs 48%) and black (55% vs 36%) compared with the catchment population. Seven-day average percent positivity among flagged decedents closely matched the trajectory of percent positivity in the catchment population, particularly during the peak of the outbreak (March and April 2020). After a lull in May to mid-June, new positive tests in late June coincided with increased case detection in the catchment. We found large racial disparities in test results; SARS-CoV-2-positive decedents were substantially more likely to be black than SARS-CoV-2-negative decedents (82% vs 51%). SARS-CoV-2-positive decedents were also more likely to be older and to have died of natural causes, including of COVID-19 disease. CONCLUSIONS: Disease surveillance through medical examiners and coroners could supplement other forms of surveillance and serve as a possible early outbreak warning sign.

Comparative study of four SARS-CoV-2 Nucleic Acid Amplification Test (NAAT) platforms demonstrates that ID NOW performance is impaired substantially by patient and specimen type.

The COVID-19 pandemic in the United States created a unique situation where multiple molecular SARS-CoV-2 diagnostic assays rapidly received Emergency Use Authorization by the FDA and were validated by laboratories and utilized clinically, all within a period of a few weeks. We compared the performance of four of these assays that were evaluated for use at our institution: Abbott RealTime m2000 SARS-CoV-2 Assay, DiaSorin Simplexa COVID-19 Direct, Cepheid Xpert Xpress SARS-CoV-2, and Abbott ID NOW COVID-19. Nasopharyngeal and nasal specimens were collected from 88 ED and hospital-admitted patients and tested by the four methods in parallel to compare performance. ID NOW performance stood out as significantly worse than the other 3 assays despite demonstrating comparable analytic sensitivity. Further study determined that the use of a nasal swab compared to a nylon flocked nasopharyngeal swab, as well as use in a population chronically vs. acutely positive for SARS-CoV-2, were substantial factors.